The demand for the refined fossil fuels is growing drastically but the supply of high-quality crude oil is depleting. It is well-established fact that the balance of crudes that need to be processed still contains a significant amount of heavy fractions. Further, due to stringent environmental norms and particularly new sulphur regulation for Bunker fuels, easy avenues for disposal of residue oil no longer exists.
Upgrading residue to value-added products can be done, according to the available literature, using any of the 3 routes, (i) carbon rejection, (ii) hydrogen addition & (iii) combination of both. Carbon rejection route includes processes such as visbreaking, solvent deasphalting, thermal cracking (coking) and Fluidized catalytic cracking (FCC). Hydrocracking is hydrogen addition route. The processes like solvent deasphalting, visbreaking, and coking, produce a significant amount of low-value by-products and their products require extensive post treatments viz. HDS, HDN, and HDM. However, due to lower investment cost, these processes are very popular. Another technology for upgrading residue is Resid FCC or RFCC. The main disadvantage of this process is that it cannot handle feeds with high CCR.
The hydrogen addition route consumes a substantial amount of hydrogen and is relatively high in investment and operating costs. However, with product specifications becoming stringent and increasing demand for diesel, the hydrogen addition routes are gaining importance.
Based on the types of the reactor the residue hydrocracking processes, in general, are classified as (i) Fixed bed hydrocracking, (ii) Ebullated bed hydrocracking and (iii) Slurry hydrocracking.
The fixed bed hydrocracking process for upgrading residue is similar to other fixed bed hydrocracking processes, where the feed and hydrogen are passed over the catalyst bed at a particular temperature and pressure. However, because of the much higher level of impurities (metal, asphaltene etc.) in the residue compared to other distillates, the operation of fixed bed process is not easy as compared to other fixed bed processes. The asphaltene molecules in vacuum residue remain in suspended form. The stability of this colloidal mixture may get disturbed due to any physical and/or chemical changes and may lead to precipitation of the asphaltene molecules. This phenomenon is called phasing out of asphaltene. Because of the high level of impurities and simultaneous phasing out of asphaltene from the solution, the ΔP across the catalyst bed increases very rapidly for fixed bed residue hydrocracking. In fixed bed hydrocracking process, the problem of high level of impurities is generally handled by multiple trains of treating reactors and the problem of phasing out of asphaltene molecules is addressed by reducing the overall conversion.
Ebullated bed reactors are one of the types of fluidized bed reactor that utilizes ebullition, or bubbling, to achieve an appropriate distribution of reactants and catalysts. The ebullated bed is mostly applicable for the feedstocks which are difficult to process in fixed-bed or plug flow reactors due to high levels of contaminants. The ebullated bed reactors offer high-quality, continuous mixing of liquid and catalyst particles and have the characteristics of the stirred reactor. The catalyst used for the ebullated bed is about 0.8-mm diameter extrudate and is held in a fluidized state through the upward lift of recycle liquid reactants and products. The liquid and gas enter the reactor plenum and are distributed across the bed through a distributor and grid plate. The height of the ebullated catalyst bed can be controlled by the rate of liquid recycle flow. The operability of ebullated unit is mainly affected by deposit formation. In residue hydrocracking process, deposit formation takes place mainly because of phasing out of asphaltene molecules. The phasing out of asphaltene molecules occurs because of incompatibility of hydrocracked products with the asphaltene molecule. The hydrocracked products have in general lower aromatic content and this tends to makes the mixture unstable and causes precipitation of asphaltene molecules. The asphaltene precipitation is controlled by limiting the conversion of residue and increasing recycling ratio. Sometimes, the stabilizers are also used for making the asphaltene molecules stable. Another, limitation of ebullated bed reactor is reaction kinetics. The order of hydrocracking reaction is between 1 and 2 and hence plug flow reactor is better than a stirred reactor. As the characteristic of the ebullated reactor is same as stirred reactor hence the conversion is affected. Further, the operability of ebullated bed reactor is much complex compared to fixed bed reactor. However, the ebullated bed reactor is preferred over the fixed bed reactor for residue hydrocracking.
Slurry reactors can process feeds with very high metal and CCR contents. Slurry reactors are basically three-phase reactors and usually consist of catalyst (solid), suspended in a liquid through which hydrogen gas is bubbled. In conventional slurry reactors, also commonly known as Slurry Bubble Column reactors, which are generally used for hydrocracking of vacuum residue, the feed, the catalyst, and hydrogen are introduced from the reactor bottom and effluent is withdrawn from the top. The reactor is basically a hollow cylinder with some arrangement for mixing and redistributing the hydrogen into the reaction mixture. Hydrocracking reaction takes place while traveling from the bottom to the top. Although the slurry reactors have an advantage of efficiently converting poor quality feedstocks compared to the other hydrocracking processes described above, it also suffers from the following disadvantages:                i. Asphaltene precipitation and choking of reactor and downstream equipment: This happens because the hydrocracked products are incompatible with asphaltene molecules because of lower aromatic concentration. As the hydrocracking reaction takes place, the delicate balance between asphaltene, resin and aromatics get disturbed and cause asphaltene molecules to precipitate.        ii. Coke formation and choking of the reactor and downstream equipment: In the conventional slurry reactor, the problem of coke formation is very critical and this happens due to improper distribution of hydrogen, agglomeration of coke precursor etc. In the present slurry reactor system, the hydrocarbon is in the continuous phase and the hydrogen is bubbled through it. This results in an improper contact between the hydrocarbon and the hydrogen which gets further deteriorated during the course of travel through the reactor.        iii. Secondary cracking: In conventional slurry reactor system, the product remains in the reaction mixture along with the unconverted feed till end in the reactor. This causes over cracking of heavy middle distillate and middle distillate to lighter hydrocarbon, particularly, light naphtha and gases.        
The deficiencies of conventional Slurry reactor system, have been addressed in the present invention.